Update infrastructure to more closely match other OpenStack projects

This patch imports nova's HACKING.rst guidelines altered for Heat.
This patch imports nova's run_pep8.sh with some minor alterations.
This patch imports nova's hacking.py extensions to pep8.

This patch places the run_pep8 logic in a separate file rather than
having it spread between tox.ini and run_tests.sh.  The HACKING.rst
requirements as well as general pep8 requirements are then enforced
with run_pep8.sh.

Avoid running once the N802 rule until dependency changelogs are
less then 50 characters.

Change-Id: If46c14668eae3cf11b8fbff46d766cc589d701aa
Fixes: Bug #1131275
Add heat-watch to pep8 checks

heat-watch was missing from pep8 checks in the past.  Tidy up heat-watch
and add to run_pep8.sh.

Change-Id: I36680b24ee90a5daeb7f8d7418b665a215026325
Fixes: Bug #1131275